1. Field of the Invention
The present invention relates to continuously variable valve actuation (CVVA) system and, more particularly, to a CVVA system in which the lift time, the lift distance and the duration of a valve can be simultaneously varied depending on various conditions of an engine, particularly the low-speed/high-speed operating range of an engine.
2. Description of Related Art
As for an engine, a camshaft is rotated by a rotating force transmitted from a crank shaft, and an intake valve and an exhaust valve are reciprocated up and down with regular timing by drive cams of the camshaft. Thereby, intake air is supplied to a combustion chamber, and combustion gas is exhausted. In this process, a fuel-air mixture is compressed and exploded to generate power.
At this time, a mechanism that can continuously vary the lift distance of a valve according to an operating speed of the engine is called a continuously variable valve actuation (CVVA) system.
Hereinafter, a conventional CVVA system will be described in detail with reference to the attached drawings.
FIG. 1 schematically illustrates the configuration of a conventional CVVA system.
Referring to FIG. 1, the conventional CVVA system includes a driving cam 4 installed on a camshaft 2, a swing arm 12 swinging in contact with the driving cam 4, a driving arm 19 driving a valve 5 in cooperation with the swing arm 12, a variable arm 13 causing the driving arm 19 to be pivoted around a swing axle of the swing arm 12, an actuator driving the variable arm 13, and a cam means installed between the swing arm 12 and the driving arm 19.
The swing arm 12 and the variable arm 13 are supported on a common control shaft 10 so as to allow relative motion. The driving arm 19 is connected to the variable arm 13 at a base end thereof, and has a driving portion 20 driving a rocker arm 6 at a leading end thereof. Further, the cam means includes a cam face 15 formed on the swing arm 12, and a cam follower 22 supported on an intermediate portion of the driving arm 19, and is configured to change an initial position of the driving arm 19 with respect to the swing arm 12 by pivoting of the driving arm 19.
According to the aforementioned configuration of the conventional CVVA system, when the driving cam 4 is rotated in a counterclockwise direction from the position illustrated in FIG. 1, the end (particularly, the right-hand end) of the swing arm 12 is rotated so as to move toward the driving arm 19 (see FIG. 1). When the end of the swing arm 12 comes into contact with the driving arm 19, the rocker arm 6 is pressed, and thus the valve 5 is opened.
At this time, when the variable arm 13 is rotated in a counterclockwise direction from the position illustrated in FIG. 1, the intermediate portion of the driving arm 19 comes into contact with the rocker arm 6, and thus gets near the end of the swing arm 12. In this state, when the driving cam 4 is rotated, the end of the swing arm 12 presses the driving arm 19 earlier, so that the valve 5 has an earlier lift time and thus a longer lift distance.
Thus, the conventional CVVA system as illustrated in FIG. 1 has an advantage in that the lift time and distance of the valve 5 can be regulated to the speed of an engine.
However, the conventional CVVA system is essentially equipped with various constituent parts such as a swing arm 12, a driving arm 19, a variable arm, an actuator 11, etc. in order to transmit the force of the driving cam 4 to the valve 5, so that it has a complicated configuration and a high cost of production.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.